This invention relates to a method for bisphenol A production by condensation of phenol with acetone in the presence of an acid ion exchangable resin catalyst.
There are known many methods for obtaining bisphenol A by the use of an acid ion exchangable resin catalyst.
In the method known from Polish Patent 96346, condensation of phenol with acetone is conducted with multiple circulation of the reaction mixture through a cation-exchange resin bed of sulfonated copolymer of styrene and divinylbenzene in three stages, with dosing of acetone to the reaction mixture which contains also recycled by-products of the reaction. This method can be performed periodically or continuously.
Further development of the above-mentioned method is described in U.S. Pat. No. 4,301,305 according to which, the process of condensation of phenol with acetone is conducted continuously in three stages in two reactors having stationary cation-exchange resin beds. The catalyst bed in each reactor is 15-20 m high and is divided into a lower zone and an upper zone. The reaction mixture is circulated through each catalyst bed in various stages of the process at various linear velocities.
The first stage of the reaction is carried out in the first reactor in sequence in the lower zone and then in the upper zone of the catalyst bed at a temperature of 60-85 degress C. The second stage of the process is carried out at a temperature of 65-90 degrees C in the lower zone of the catalyst bed of the second reactor; and the third stage of the process is carried out in the upper zone of the second reactor at a temperature of 70-95 degrees C.
The linear velocity of the reaction mixture flow through the lower zone of the catalyst bed of each reactor, does not exceed 10 m/h; and the velocity of the reaction mixture flow through the upper zone of the catalyst bed in each reactor does not exceed 4 m/h. The mixture charged to the reactors contains 11 percent by weight of bisphenol A and 10.5 percent by weight of reaction by-products. The method according to Polish Patent 96346 and U.S. Pat. No. 4,301,305 permits the reaction of phenol with acetone to be carried out with relatively high selectivity.
The method of bisphenol A production, according to U.S. Pat. No. 3,049,569 proceeds in several stages. It comprises condensation of acetone with phenol, the latter being in stoichiometric excess, in an anhydrous medium at a temperature from about 30 degrees C to about 125 degrees C in a bed of an insoluble cation-exchangable resin. A part of the acetone and the phenol in the reaction zone remains in the liquid phase between the start and the finish of the reaction. As a result, there is formed an incompletely reacted post-reaction mixture containing bisphenol A, an adduct of bisphenol A and phenol, unreacted acetone, unreacted phenol, by-products of the reaction and water. Incompletely reacted post-reaction mixture is first divided into an upper stream containing acetone, water and phenol and a lower stream containing bisphenol A, the adduct of bisphenol A and phenol, and the by-products of the reaction. The upper stream is dehydrated and substantially anhydrous phenol and acetone are recycled to the reaction zone. From the lower stream there is separated the adduct of bisphenol A and phenol; and the remaining part of the lower stream is recycled to the reaction zone. Next, bisphenol A is separated from its adduct with phenol, and the phenol is recycled to the reaction zone. The characteristic features of this method are recycling of the by-products of the reaction to the reaction zone in order to reduce their formation and the use of single flow of the reaction mixture through the cation-exchange resin bed with a short residence time in the reaction zone.
Under these conditions 50 percent of the acetone is reacted and the reaction is carried out with a concentration of bisphenol A between 4-6 percent by weight in the charge mixture to the reaction zone and 12-14 percent by weight in the post-reaction mixture.
Recycling of the by-products of the reaction to the reaction zone was expected to influence their level at about 8 percent by weight in the reaction mixture, which would enable high selectivity of the reaction of phenol with acetone.
However, in industrial practice it appears that, in spite of considerable advantages such as the high efficiency of the reaction based on the catalyst volume and the simplicity of the technological process, the method of bisphenol A production according to U.S. Pat. No. 3,049,569 did not provide appropriately high selectivity of the reaction of phenol with acetone and the required purity of the desired product. It also appeared that it was impossible to achieve the assumed state of equilibrium for some by-products of the reaction, for instance, for the o-p-bisphenol A isomer and that the process could not be performed for a long period of time without loss of a considerably quantity of by-products of the reaction.
Proof for the above-mentioned fact is the method disclosed in U.S. Pat. No. 3,221,061 which method comprises exposing the by-products of the reaction to a cation-exchange resin for their partial isomerization and rearrangement, with resulting reduction of the by-products of the reaction. However, this procedure did not solve the problem completely since additional decomposition of some by-products of the reaction in the presence of an alkaline catalyst is required for improvement of the general selectivity of the process.
In spite of so many improvements of the method of bisphenol A production known from U.S. Pat. No. 3,049,569, it is still subject to relatively low selectivity with simultaneous high energy consumption resulting from low concentration of bisphenol A in the post-reaction mixture and the necessity to handle a large quantity of diluted phenol solution.
An improvement of the above-discussed process is described in U.S. Pat. No. 4,308,405 and comprises recycling a part of the stream obtained by drying of the post-reaction mixture to the reaction zone in order to reduce the quantity of phenol to be removed by evaporation from the post-reaction mixture before bisphenol A is separated from it.
A further attempt to improve the process selectivity is described in U.S. Pat. No. 4,391,997 and comprises increasing the temperature of the reaction mixture as its passes through the reaction zone in order to reduce formation of by-products of the reaction and to improve the color of the reaction mixture.
This method, which is similar to the above-mentioned methods known from Polish Patent 96346 and U.S. Pat. No. 4,301,305, basically differs from them in that it deals with a single flow of the reaction mixture through the cation-exchange resin bed.
The above-mentioned facts show that the problem of selectivity of the reaction of acetone with phenol to form bisphenol A in the presence of a cation-exchange resin catalyst has not been solved to a satisfactory extend and that the consumption of phenol and acetone still differs considerably from the stoichiometric data.